Spin valve ("SV") heads (sometimes referred to as giant magneto resistive heads or "GMR" heads) are very attractive for use as high density recording magneto resistive ("MR") rip heads because of their high readback output voltages, linear response, and symmetrical read sensitivity profiles. FIG. 1 shows an air bearing surface view of a prior art SV sensor 10 comprising end regions 12 and 14 separated by a central region 16. A free layer (free ferromagnetic layer) 18 is separated from a pinned layer (pinned ferromagnetic layer) 20 by a non-magnetic, electrically-conducting spacer layer 22 (typically, primarily copper). The magnetization of the pinned layer 20 is fixed through exchange coupling with an antiferromagnetic (AFM) layer 24. The magnetization of the free layer 18, however, is free to rotate in the presence of an external field. Free layer 18, spacer layer 22, pinned layer 20 and the AFM layer 24 are all formed in the central region 16. Hard bias layers 26 and 28 formed in the end regions 12 and 14, respectively, provide longitudinal bias for the MR free layer 18. Leads 30 and 32 formed over hard bias layers 26 and 28, respectively, provide electrical connections for the flow of the sensing current Is, from a current source 34 to the SV sensor 10. A signal detector 40 which is electrically connected to the leads 30 and 32 senses the change in resistance of the SV sensor 10 due to changes induced by the external magnetic field (e.g., the field generated by a when a field transition on a disk is moved past the SV sensor 10. In the example of FIG. 1, a cap 42 is optionally provided.
During the manufacturing of a read/write head for magnetic recording media, the write head may be formed on top of the SV sensor 10. During the manufacture of the write head, and during some of the processes involved in manufacturing the SV sensor 10, itself, high temperature processes have inevitably been involved. (Examples are the photoresist baking of the write head, the annealing of the AFM layer 24 material which is required for some materials, and resetting of the pinned layer 20.) At these temperatures, the grain boundaries of adjacent materials tend to become aligned, notably at the junction of the spacer 22 and the free layer 18 and/or at the boundary of the spacer 22 and the pinned layer 20. In this condition, it is very easy for diffusion between such layers to occur. This results in a degradation of the output signal amplitude produced by the SV sensor 10.
Clearly, it would be desirable to prevent the degradation caused to longer term thermal treatment of the spin valve head during the manufacturing process. However, to the inventor's knowledge, no prior art construction or process has effectively and sufficiently reduced the reduction of spin valve output amplitude caused by such thermal treatment.